There has been proposed a technique (referred to as “a high-speed duplex printing”) for improving a speed of the duplex printing process by printing N sheets (N is a positive integer) on the first side thereof and subsequently printing M sheets (M is an integer equal to or more than 0) on the second sides thereof. For example, for performing duplex printing on 10 pages (5 sheets), an image forming apparatus prints them in the page order of 2 (even page), 4 (even page), 1 (odd page), 6 (even page), 3 (odd page), 8 (even page), 5 (odd page), 10 (even page), and 7 (odd page), and 9 (odd page). Furthermore, an image forming apparatus prints them in the page order of 1, 3, 5, 2, 7, 4, 9, 6, 8, and 10.
However, the above-described duplex printing technique has the following problems. Specifically, high-speed duplex printing during which the sheets are caused to stay in the apparatus as mentioned previously can be improved in terms of an operating mode achieved when a request for image quality adjustment is received during the duplex printing.
For example, in relation to image adjustment on positional displacement or density deviation, correction process includes forming a test image on an image carrier, measuring the inspection image, and determining new correction data in accordance with a result of measurement. A conceivable operating mode employed during such correction process is to output sheets staying in the apparatus when the request for image adjustment is received and to perform correction process while printing is suspended. However, the operating mode entails temporary suspension of conveyance of a sheet during high-speed duplex printing, which in turn involves consumption of a time for outputting sheets in a conveying path and time for feeding a new sheet. Meanwhile, an operating mode disregarding correction process causes degradation of image quality.